Dwyer GFC - Manual (Page 14)

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CAUTION: If the valve is left in the AUTO (control) or OPEN (PURGE)
mode for an extended period of time, it may become warm or even hot
to the touch. Use care in avoiding direct contact with the valve during
operation.
Do not run GFC-110/111/113/114 for extended periods of time with the valve in
AUTO or PURGE mode without the flow of gas through the transducer. Doing so
may result in up to 2% f.s. shift in calibration.
5.2 Flow Signal Output Readings
The flow signal output can be viewed either on the LCD display, remote panel
meter, digital multimeter, or other display device used as shown in figure 2.a.
If an LCD display has been ordered with the GFC, the observed reading is in
direct engineering units. Such as 0 to 10 sccm or 0 to 100 slpm (0 to 100% indi-
cation is optional). Engineering units are shown on the flow transducer's front
label.
Analog output flow signals of 0 to 5 VDC and 4 to 20 mA are attained at the appro-
priate pins of the 15-pin "D" connector (see Figure 2-a) on the side of the GFC
transducer.
Meter signal output is linearly proportional to the mass molecular flow rate of the
gas being metered. The full scale range and gas for which your meter has been
calibrated are shown on the flow transducer's front label.
The default calibration is performed for 0 to 5 VDC input/output signal. If 4-20
mA output signal is used for flow indication on the GFC, which was calibrated
against 0 to 5 VDC input signal, the accuracy of the actual flow rate will be in the
specified range (+1.5%) of full scale, but the total uncertainty of the output read-
ing may be in the range of +2.5% of full scale. Optional calibration for 4-20 mA
output signal is available upon request at time of order.
For optional RS232 or IEEE488 interfaces please contact your distributor or
Dwyer.
5.3 Swamping Condition
If a flow of more than 10% above the maximum flow rate of the Mass Flow
Controller is taking place, a condition known as "swamping" may occur. Readings
of a "swamped" meter cannot be assumed to be either accurate or linear. Flow
must be restored to below 110% of maximum meter range. Once flow rates are
lowered to within calibrated range, the swamping condition will end. Operation of
the meter above 110% of maximum calibrated flow may increase recovery time.
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